AGM Battery Install close to 3 way fridge?

"Hydrogen is considered flammable if the concentration in air reaches 4%, or about 1kg in the example above.
The battery would need to be continuously charged for 100,000hrs for the H2 concentration to become dangerous inside the van"

- this calculation assumes that the gas from the battery will be distributed equally through the space - I see no reason to assume that.

All "sealed" batteries that are installed in an unventilated space e.g, car boot, have a vent tube from the battery to ensure all gases go outside.

Mike,

I think it's worth thinking this through, based on some scientific research.

H2 disperses within seconds in a given volume of air.
Take a look at this study, the last page in particular.
H2 dispersion in air
The blue volume inside the 2.9x1.22x0.74 m^3 vented air space shows a concentration of 4%.
It takes ~6 seconds for the gas to fill the air space after which equilibrium (gas generation rate equals gas venting rate) sets in.
I estimate the blue volume taking up 10% of total space, or around 260 litres.
You need to keep the H2 production rate at 260*0.04l/6s, or 1.7l/s to keep up with the venting rate.
If not, the 4% H2/air mix will drop in volume until a new equilibrium is reached, i.e. the amount of flammable gas will drop.
Now, under a worst case scenario, a gassing VRLA battery which gets overcharged with a current of around 20A, emits H2 at a rate of approximately 1g/hr - equivalent to 0.0039l/s. Compare this with the 1.7l/s figure and it'll become clear that the amount of flammable gas inside the air space will be very small. I guess that due to the limited amount of flammable gas it'll mainly concentrate around the battery, and the slightest air movement (like heat convection) will disperse the gas further which'll make the concentration drop well below 4%.

And if the overcharging goes unnoticed, the battery might indeed heat up and swell, but the pressure inside will never go above 4 to 6 psi which is the opening pressure of the valves.
So in the end, the swollen battery will be full of steam and oxygen/hydrogen which might go off like a fire cracker if some flame next to it is present AND if it really ruptures.
A well vented battery compartment is recommended which'll muffle the sound a bit.
Is this life threatening?
I don't think so.

cheers, Peter

. . . and are you going to show us your calculations that prove that playing Russian Roulette is totally safe ???

Hi Chris

Take note of Derek's advise
,separate isolated, vented compartment.

I am afraid I cannot agree with Peter's figures . He talks about the whole van volume which is irrelevant.
Totally disagree with this:"Thus, there is no problem having A BATTERY installed near a 3 way fridge. "
ANY BATTERY ???


The fridge compartment air space would be small ,so his figures are invalid.

Peter

@Derek,

If a battery expands like that while it's not being charged, there need to be a number of concurrent faults:

1) An internal short which creates enough heat to boil off some of the water inside the battery.
2) The overpressure valves open on a regular basis every time the battery gets re-charged. This doesn't seem to be the case with this battery because the internal pressure obviously was enough to bulge the walls at this relatively low wall temperature of 49 degrees. There is already a discrepancy: steam pressure only develops near 100 degrees, but the case temperature was only measured being 49 degrees, a temperature gradient of 50 degrees inside a few mm thick plastic wall?
3) Note that the battery is visibly swollen on 3, possibly 4 sides. That means that not only one cell failed but likely all six of them.
Considering that each cell has its own overpressure valve, all six valves must have failed concurrently.

So there was a failure in a number of cells, plus in a number of overpressure valves?
I don't want to have a crack at the odds for something like this to happen in a single occurrence.

And then, the author admits to have had 3 swollen batteries by different manufacturers within the space of one month...

Hmm, if it was me I'd toss out my battery charging gear - or maybe he uses his beloved DC arcwelder for charging and glued the overpressure valves shut to stop them from making annoying noises?

@oldtrack123,

the whole van airspace is not irrelevant because the highly volatile hydrogen gas will quickly disperse after escaping from the battery, within this volume AND beyond, i.e. to the outside.

And I don't have to mention that a pilot flame needs to be placed in a vented space otherwise it would simply run out of oxygen.
This vented space is more than enough to also vent any traces of hydrogen escaping from the battery, yes that's ANY battery for that matter (VRLA batteries are a bit safer in this regards, because the pathway for external flames to the inside is restricted by the valves - just in case someone wanted to try this by pointing a flame at the vents/valves).

Back to the vented space of the pilot, at this extremely low concentration of H2 gas outside the battery, no flame in the world will ignite it, so the traces of H2 will safely vent together with the hot combustion products of the pilot flame.

You'd have to forcefully open the battery and ignite the gas inside at the same split second of opening it - before all the combustible hydrogen's gone - if you wanted to make it go bang.

How many folks keep their batteries inside a caravan, where there are all sorts of naked flames i.e. pilot flames, gas cookers, lighters...
Can you give me one single example where it has been proven that the tiny traces of hydrogen escaping from a battery have built up sufficiently inside a van to cause an explosion?

And please kindly note that in the linked example of a swollen battery, the culprit is steam pressure and not hydrogen...

cheers, Peter

Hi Chris

Please insulate and vent that 'cavity'.

I would not mount any battery close to a gas pilot flame.

Regards

Derek from ABR

From a slightly different perspective, the further the battery is from its charging source (assuming the tug alternator) considerably heavier cable to overcome voltage drop is required otherwise you will have greatly reduced charging efficiency.
In over 60yrs. of experience with batteries (home 32v. system originally) I have only ever seen the result of one battery explosion.
This was when an alligator clip was removed from a battery whilst the charger was still switched on.
Not a good look!
mike

Could Battery Value explain why it is said that it is a bit too hot under a bonnet

for some types of batteries but it is ok to locate it close to a burning flame.

Seems a bit of common sense is needed here.

Even batteries mounted in a van boot are supposed to be vented to the outside..

Dont want 6ins of technicalities just a straight answer.


It is apparently illegal to mount batteries in the living area INSIDE a caravan as far as I know

Yes its done by unscrupulous manufacturers but time they didnt.

I had a similar issue with a sla battery in my home security system. I attempted to charge a spare battery directly from the transformer, but, I connected it in reverse polarity. the battery heated up and expanded similarly to the one in the photo - boy did that get my immediate attention - if the battery had blown on the new kitchen bench the minister for war would have had a mandate???. It was just stupid of me to do this, but it was so simply done. I am thankful that the battery was on the bench and being monitored by me....one of the smarter things I did that day. Lesson learned.

Below is am AGM battery marketed as 12V 50Ah 690CCA deep cycle VRLA AGM battery.

Please note the warnings on this battery label, in particular the ones showing warnings about open flames and explosion.

Image Could Not Be Found

While I was browsing the same website I found this AGM.

Note the warnings on the battery too...

Image Could Not Be Found

So my recommendation is...

Please insulate and vent that 'cavity'.

Thank you Derek and Peter and others for your advice. I will reconsider my battery installation so that we will be 100% safe in our camper trailer.


Thanks
Chris.

You're most welcome Chris.

Some closing words are in order:

I think some folks got a bit carried away by spectacular looking photos etc.

To put things into perspective:

Chris' original post read about the intention of putting an AGM battery in a cavity next to the 3 way fridge.

So this would mean a separate cavity from the fridge cavity right?
Because usually the fridge cavity is taken up by the fridge itself leaving no room for an additioanal battery in there.

Then Derek quite rightly recommended to vent that battery cavity which is good advice, because no battery must be operated in a gas tight cavity due to the possibility of hydrogen buildup which could ignite by someone pointing a flame at it, or by sparks at the terminals due to lose connections etc.
The example given by Mark39 quite likely involves a vented wet cell battery type which indeed offers a pathway from the outside to ignite the gas trapped inside the battery.

On VRLA batteries, this pathway to the inside is restricted by flame restricting valves (wouldn't test this necessarily by pointing a flame at the valves during heavy charging though).
So how you would make a pilot flame pointing at the valves of an AGM which are usually mounted along the top of the battery is beyond my imagination.

@ Graham H:

No I don't think that's even close to 6 inches of technicalities - although I like the way you express it (don't let a few numbers scare you), and here comes my straight answer: you can mount any VRLA safely inside a van - except right on top of (ok, and directly next to) the pilot flame just in case somebody thinks someone's recommended this spot for mounting a battery.

cheers, Peter

Here is NSW Fire & Rescue's analysis of what can cause sealed VRLA batteries to expand like this -

"Several conditions can cause the battery to heat up, such as HIGH AMBIENT TEMPERATURE, POOR VENTILATION, incompatible charging equipment, charger malfunction and battery cell failure.

Generally, gas is not produced during charging. However, if a battery is overcharged due to charger malfunction or battery failure, gas pressure can build within the battery. A pressure relief valve is designed to release the excess hydrogen and oxygen."

- from http://downeasteryachts.com/archives/2134